1. Field of the Invention
The present invention relates to a device and method for injecting a medication into a pressurized pulmonary respiration system. More particularly, the invention relates to a medication delivery device and method for pulmonary dosing in a Continuous Positive Airway Pressure (CPAP) system.
2. Background of Related Art
Many respiratory conditions and diseases exist which are treatable by the administration of oxygen or oxygen-enhanced air. Several examples of such are Chronic Obstructive Pulmonary disease (COPD), congestive heart failure (CHF), and asthma. Asthma is sometimes categorized as a COPD.
Chronic Obstructive Pulmonary disease (COPD) is a condition in which a patient's lung has limited elastic recoil and/or the alveoli and terminal bronchioles have stiffened with scar tissue. The terminal bronchioles may collapse during exhalation, leading to air trapped in the alveoli. The disease causes much discomfort inasmuch as a patient must work hard to breathe, and physical exercise is difficult.
Congestive heart failure (CHF) may result in “preload” in which the blood sent to the left ventricle by the lungs exceeds the heart's capacity. Alternatively, the pressure against which the heart is pumping may be excessive, a condition called “afterload”. As a result of either or both conditions, a patient will lose the ability to absorb oxygen and get rid of carbon dioxide.
In any of the pulmonary diseases and conditions, a loss of oxygenation may reach a critical state requiring emergency treatment. Typically, emergency treatment must begin without delay, and equipment and medicinals for administering treatment are normally available in an emergency vehicle such as an ambulance. Depending upon the particular disease and condition of the patient, one or both of oxygenation and medication are commonly applied.
Other relatively common respiratory conditions exist, including for example, apnea, in which a patient has an absence of breathing. When it occurs during sleep, the condition may be fatal.
In addition to specific medicinal treatments, emergency treatment of respiratory distresses may include one or more of resuscitation, opening of an airway blockage for ventilation, and oxygen enhancement via nasal catheter, mask or endotracheal catheter. More complex systems are capable of increasing ventilation and oxygenation of a patient during the inhalation portion of the breathing cycle, but because of their complexity are not generally made available to emergency medical technicians (EMT's). An example of such a system is a Bi-level Positive Airway Pressure (BiPAP) system, in which a respiration machine senses the onset of a patient's inhalation cycle and elevates the pressure in the patient's airway for enhanced inhalation. The exhalation pressure is typically reduced.
The numbers of medical personnel in an ambulance is typically very limited, and the purpose is to transport a patient to a permanent medical facility quickly, performing only basic medical procedures required to protect the patient's life. Even a relatively minor invasive procedure such as ericothyriodotomy is not performed in a pre-hospital setting unless absolutely necessary to the life of the patient. Typically, such a procedure is an advanced skill performed by a medical doctor, flight nurse, or paramedic. This is not a skill performed by an emergency medical technician (EMT), as governed by standards of the profession. Currently, endotracheal intubation is indicated when a patient cannot oxygenate himself adequately, the “gag” reflex is gone, or a patient's breathing has stopped. In endotracheal intubation, a patient's airway is visualized, and a tube is inserted. Breathing is then taken over by manual assistance or mechanical ventilator. Hazards associated with endotracheal intubation include hypoxia, aspiration, trauma to the airway, and an acquired dependency of the patient to the ventilator. Therefore, intubation is generally not performed unless absolutely necessary.
In the practice of respiratory treatments, available face masks are designed to provide oxygen/air through the mouth and nostrils of a patient, and assume that in the event a nebulized medication is to be administered, the patient's head and upper body will be raised i.e. substantially upright. Thus, the centerline axis of the mask's inhalation port is substantially parallel to the patient's longitudinal axis, i.e. nearly horizontal when the patient is in a supine position. A nebulizer's outlet is constructed to fit rigidly into the mask's inhalation port, and a patient is supported in an upright position during the administration. However, in an emergency situation in which the patient's condition (severe injury/illness) requires a supine position, a way must be found to administer a nebulized medication at a controllable rate and without undue stress to the patient. Attempts to administer a medication aerosol to a face mask of a supine patient may result in non-delivery and wastage of a substantial portion of the medication due to flooding of the nebulizer. The un-aerosolized medication may be carried over into the mask and discharged. Thus, a patient is deprived of much of the medication.
In emergency medical pre-hospital situations, time is usually a critical factor. Typically, emergency i.e. pre-hospital personnel make a rapid diagnosis to determine what procedures are required to maintain life and prevent patient deterioration during transit to a treatment center, e.g. hospital. Emergency personnel must determine whether respiratory treatment is indicated, and if so, whether the indicated treatment is to be minimal, such as the simple application of a stream of oxygen or oxygen-enriched air ( e.g. such as 21-90 percent oxygen) by mask or nasal cannula, or when a more invasive technique requiring endotracheal intubation is indicated.
In most breathing emergencies, a variety of medications such as bronchiodilaters (e.g. albuterol) may be indicated, depending upon the diagnosis protocol. Providing oxygen through an endotracheal catheter has a number of disadvantages relating to simultaneous or co-medication of the patient. In order to apply an aerosolized medication, the endotracheal tube may be removed from a ventilatory source to inject the desired medication. Often, multiple doses of more than one type of medication may be required, leading to less than optimal ventilation/oxygenation as well as irritation of the patient's throat. In some emergency situations, continuous application of both oxygen and medicinals may be indicated, in which case the emergency personnel must attempt to provide both oxygen and medicinals with minimal downtime for each. In some cases, adequate oxygenation/respiration and adequate medication delivery cannot be both maintained, leading to extreme stress to the patient, and deterioration of the patient's condition.
In the past few years, another technique has been developed which is intermediate simple oxygenation and the more radical procedures requiring endotracheal intubation. The method has been used for many years in some fixed installations (e.g. hospital emergency rooms) but not generally in emergency vehicles. This method is known as Continuous Positive Airway Pressure (CPAP) and is appropriate for patients suffering severe respiratory distress for which normal oxygenation/respiration at atmospheric pressure is less than effective. Prior to the availability of emergency CPAP treatment, the patient was typically subjected to endotracheal intubation, a much more invasive procedure. A current protocol for the use of CPAP is summarized in a reference in PARAMEDIC 01/03, page 3C entitled CPAP.
In the CPAP method, a continuous positive internal pressure is applied to the patient's airway during both inhalation and exhalation. As shown in FIG. 1 of the drawings, a simple CPAP apparatus 100 of the prior art includes an oxygen source 102 capable of delivering a pressurized stream of oxygen 104 or oxygen diluted to a lower concentration, such as for example 25-90 percent. A gas diluting apparatus 106 may be used to dilute a nearly pure oxygen stream 104 with filtered atmospheric air 108 to a desired concentration using aspiration, thus reducing the weight of pressurized gas which must be carried aboard an emergency vehicle. A tightly-fitting mask 110 is required to prevent undue leakage at the mask-face interface 134, and to maintain a desired airway pressure. The CPAP face mask 110 has an inhalation port 112 and an exhalation port 114, the latter having a Positive End-Expiratory Pressure (PEEP) valve 116 which maintains a positive pressure in the mask and patient's airway. Often, a filter is incorporated into the PEEP valve 116 to prevent escape of exhaled fluids, etc. into the atmosphere. The maintained pressure is typically between about 5 cm. water and about 15 cm. water but may be higher or lower, for example, from about 2 cm. water to about 30 cm. water, or even higher, depending upon the pressure requirement for maintaining the airway of the patient in an open condition. This pressure offsets (at least partially) the pressure against which the patient must work to inhale, and maintains an open airway in exhalation. In COPD patients, the enhanced pressure prevents collapse of the terminal bronchioles, enhancing the exchange of oxygen and carbon dioxide. In a patient experiencing congestive heart failure (CHF), the enhanced constant pressure decreases myocardial workload while nitroglycerin is administered to dilate the arteries. Arterial dilation reduces both preload and afterload on the heart.
A Continuous Positive Airway Pressure (CPAP) treatment protocol is being considered for widespread use by emergency vehicle EMT-rated personnel, inasmuch as this method may avoid the use of invasive endotracheal intubation by endotracheal catheter. In addition, the CPAP method is straight-forward, does not require complex equipment, and is relatively easy to pre-indicate, administer, and moniter. Although CPAP has been used in hospital settings for years, the method has now been very successfully tested in some emergency vehicle venues for administration by EMT-rated personnel. General information regarding the CPAP methods and proposed use in emergency vehicles is provided in Use of CPAP and BiPAP in Acute Respiratory Failure, pp. 1 and 2 (author unknown), found at http://www.theberries.ns.ca/archives/CPAP.html.
The administration of an aerosol medication while maintaining a CPAP positive pressure of air or oxygen-enhanced air in the patient's airway represents a drawback of the current CPAP method. Typically, to dose with a medicinal aerosol, the pressurized mask is temporarily removed, and medication administered by a hand-held nebulizer or through a nebulizer mask until the medication 160 in the nebulizer jar 142 is depleted, at which point the hand-held nebulizer is removed and the CPAP mask reattached and started for oxygenation/ventilation.
Optionally, the CPAP oxygen/air stream is disconnected from the CPAP face mask and replaced by a nebulizer outlet port. Thus, the aerosol is introduced during a time when gas pressure may be insufficient to keep the airway open, or the quantity of oxygen may be too low. As a result, much of the medication may be wasted. Furthermore, the period without positive pressure may significantly reduce ventilation/oxygenation, i.e. starving the patient of oxygen. Thus, a loss of positive pressure during the medication administration period may have serious consequences. In current practice, nebulisation of a single medication dose may take up to 3-4 minutes or longer.
In addition, this method requires the patient's head to be in an upright, i.e. erect position, as described in a protocol in PARAMEDIC 01/03 entitled Pulmonary Edema. This position may be difficult to attain or maintain, and tipping of the nebulizer container e.g. jar 142 from a vertical position may have deleterious medical consequences. If a patient's head is not kept upright (see prior art FIG. 3), the nebulizer (firmly attached to the mask) will be tipped from a normal vertical position, interrupting or reducing gas flow through the medication. Aerosolization of the medication will cease or become reduced. Furthermore, tipping of the nebulizer container 142 may allow the liquid medication to flow from the nebulizer outlet without being aerosolized.
An improved procedure has been proposed by Keith Wesley, MD, in MASK CPAP FOR THE EMT-BASIC in EMS Professionals, May-June, 2003, pp. 1-3 whereby the nebulizer is positioned in-line with the bulk CPAP oxygen stream, using the oxygen stream to nebulize the medication, as depicted in Prior Art FIG. 3. However, this method prevents independent control of (a) the flowrate and pressure of the CPAP oxygen-enhanced stream and (b) the flowrate and nebulizer pressure drop of the nebulizing stream. This method may limit the total gas flow rate to the capacity of the nebulizer, which may be inadequate for proper CPAP operation. In addition, this method requires that the patient's head 150 must be positioned in a substantially upright position. Such is not always possible in a pre-hospital emergency situation because of injuries and/or illness, limited time, limited personnel, limited equipment, and/or for other reasons. As illustrated in FIG. 3, when the nebulizer cannot be maintained in a “top-side up” vertical position, liquid medication will not be aerosolized and may be largely wasted. The Wesley reference points out that in the recommended procedure, faster nebulization occurs, but “some of the medication condenses in the tubing or leaks out the PEEP valve”.
U.S. Pat. No. 4,020,834 dated May 3, 1977 to Bird discloses a respiration apparatus for treating patients in a BiPAP manner, maintaining a positive pressure during exhalation and substantially atmospheric pressure during inhalation. The apparatus and its operation are very complex. The administration of medication in a Continuous Positive Airway Pressure (CPAP) apparatus is not in view.
U.S. Pat. No. 5,287,849 dated Feb. 22, 1994 to Piper et al. discloses a medicinal aerosol delivery system for a patient's lungs. The apparatus is directed to endotracheal use and is not meant for use in a CPAP operation.
U.S. Pat. No. 6,805,118 dated Oct. 19, 2004 to Brooker et al. describes a pulmonary dosing system and method in which a medication is administered in pulsed doses entrained in air. The administration to a patient continuously maintained at a positive pressure is not in view.
None of the cited prior art documents patents provide a method for administering a medication during CPAP respiration in which the patient's head is in a non-upright position. None of the cited art overcomes the problems presented by administration of a medicinal aerosol to a patient undergoing emergency CPAP therapy, such problems including patient stress resulting from excessive time without positive pressure, insufficient exposure to medication aerosol, dumping of the liquid medication into the mask or mouth, and other incidents which may likely occur.
Efforts to overcome the disadvantages of the prior art with respect to the administration of medications during emergency CPAP have led to the effective apparatus and methods of the invention which are herein described, illustrated and claimed, infra.